1. Field of the Invention
This invention relates to an .alpha.-cyano-3-phenoxybenzyl 2-(4-chlorophenyl)isovalerate having a higher insecticidal and acaricidal activity, a process for preparing the same, and an insecticidal and acaricidal composition. More particularly, the present invention relates to an .alpha.-cyano-3-phenoxybenzyl 2-(4-chlorophenyl)isovalerate which consists substantially of or is rich in (S)-.alpha.-cyano-3-phenoxybenzyl (S)-2-(4-chlorophenyl)isovalerate and (R)-.alpha.-cyano-3-phenoxybenzyl (R)-2-(4-chlorophenyl)isovalerate.
2. Description of the Prior Art
.alpha.-Cyano-3-phenoxybenzyl 2-(4-chlorophenyl)isovalerate of the formula (I): ##STR1## has a low toxicity to mammals and a broad range of insecticidal activity (e.g., as disclosed in Japanese Patent Application (OPI) No. 26425/74[the term "OPI" as used herein refers to a "published unexamined Japanese patent application"], and U.S. Pat. No. 3,996,244) the compound contains two asymmetric carbon atoms in the molecule (designated by an asterisk (*) in formula (I)) and, therefore, includes four optical isomers.
In this specification, .alpha.-cyano-3-phenoxybenzyl 2-(4-chlorophenyl)isovalerate and its isomers will be identified as follows: .alpha.-cyano-3-phenoxybenzyl 2-(4-chlorophenyl)isovalerate of the formula (I) above will be referred to hereinafter as "fenvalerate", (R, S)-.alpha.-cyano-3-phenoxybenzyl (S)-2-(4-chlorophenyl)isovalerate will be referred to as "fenvalerate A", (S)-.alpha.-cyano-3-phenoxybenzyl (S)-2-(4-chlorophenyl)isovalerate will be referred to as "fenvalerate A.alpha.", (R)-.alpha.-cyano-3-phenoxybenzyl (S)-2-(4-chlorophenyl)isovalerate will be referred to as "fenvalerate A.beta.", (S)-.alpha.-cyano-3-phenoxybenzyl (R)-2-(4-chlorophenyl)isovalerate will be referred to as "fenvalerate B.alpha.", (R)-.alpha.-cyano-3-phenoxybenzyl (R)-2-(4-chlorophenyl)isovalerate will be referred to as "fenvalerate B.beta.", the mixture of fenvalerate A.beta. and fenvalerate B.alpha. will be referred to as "fenvalerate X", and the mixture of fenvalerate A.alpha. and fenvalerate B.beta. will be referred to as "fenvalerate Y".
The relationship between the absolute configurations of the asymmetric carbon atoms on the acid moiety and alcohol moiety to the insecticidal activity of the compounds has already been reported. The following references describe fenvalerate A.alpha., having S-configurations at the asymmetric carbon atoms on both acid and alcohol moieties, as the most active stereoisomer of the four. See Miyakado et al., Agr. Bio. Chem., 39, 267 (1975); Japanese Patent Application (OPI) No. 24019/78 (corresponding to U.S. Ser. No. 825,570, filed Aug. 17, 1977); Japanese Patent Application (OPI) No. 59646/78; Ohno et al., J. Pesticide Science, 2 (Special Issue), December 1977; and Aketa et al., Agr. Bio. Chem., 42, 895 (1978).
In the case of esters of .alpha.-cyano-3-phenoxybenzyl alcohol and a dihalovinylcyclopropanecarboxylic acid, for example, cypermethrin (NRDC-149), i.e., .alpha.-cyano-3-phenoxybenzyl 2,2-dimethyl-3-(2,2-dichlorovinyl)cyclopropanecarboxylate, and .alpha.-cyano-3-phenoxybenzyl 2,2-dimethyl-3-(2,2-dibromovinyl)-cyclopropanecarboxylate, the S-isomers of the alcohol moiety in the esters are more active than the R-isomers thereof. Racemization (or epimerization) of .alpha.-cyano-3-phenoxybenzyl esters of d-cis-2,2-dimethyl-3-(2,2-dibromovinyl)-cyclopropanecarboxylic acid and d-cis-2,2-dimethyl-3-(2,2-dichlorovinyl)-cyclopropanecarboxylic acid in the presence of a basic catalyst has been reported and, furthermore, S-isomer esters of the alcohol moieties have been obtained from the ester having RS-alcohol and d-cis isomer of these dihalovinylcyclopropanecarboxylic acids as described in Belgian Patent No. 853,866 (1977) and Belgian Patent No. 853,867 (1977).
Although these patents claim the "chiral acid" ester in the examples, only cases of d-cis-dihalovinylcyclopropanecarboxylic acid esters are shown. Particularly, in the latter case, one stereoisomer must crystallize selectively from the solution of the mixture with the enantiomer; therefore every "chiral acid" ester isomer cannot be obtained.
In the case of fenvalerate, the epimerization of the alcohol moiety of the optically active fenvalerate and the processes for obtaining fenvalerate A.alpha. from fenvalerate A by a selective crystallization or crystallization combined with simultaneous epimerization have been applied for in U.S. application Ser. No. 922,476, filed July 7, 1978 (corresponding to British Application No. 29,114/78). However, in these methods for obtaining fenvalerate, the optical resolution of the carboxylic acid is necessary, for example, these methods involve the reaction with an optically active base, the selective crystallization of a diastereomer salt, the purification of the salt and the decomposition of the salt. Furthermore, the enantiomeric acid by-product must be reused, for example, after racemization. On the other hand, the racemization of the useful acid or derivatives thereof must be avoided and, as a result, the reaction conditions are limited.